326 lines
8.8 KiB
Go
326 lines
8.8 KiB
Go
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// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build linux
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package fsnotify
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import (
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"errors"
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"fmt"
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"io"
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"os"
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"path/filepath"
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"strings"
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"sync"
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"unsafe"
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"golang.org/x/sys/unix"
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)
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// Watcher watches a set of files, delivering events to a channel.
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type Watcher struct {
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Events chan Event
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Errors chan error
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mu sync.Mutex // Map access
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cv *sync.Cond // sync removing on rm_watch with IN_IGNORE
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fd int
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poller *fdPoller
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watches map[string]*watch // Map of inotify watches (key: path)
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paths map[int]string // Map of watched paths (key: watch descriptor)
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done chan struct{} // Channel for sending a "quit message" to the reader goroutine
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doneResp chan struct{} // Channel to respond to Close
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}
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// NewWatcher establishes a new watcher with the underlying OS and begins waiting for events.
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func NewWatcher() (*Watcher, error) {
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// Create inotify fd
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fd, errno := unix.InotifyInit()
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if fd == -1 {
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return nil, errno
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}
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// Create epoll
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poller, err := newFdPoller(fd)
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if err != nil {
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unix.Close(fd)
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return nil, err
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}
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w := &Watcher{
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fd: fd,
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poller: poller,
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watches: make(map[string]*watch),
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paths: make(map[int]string),
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Events: make(chan Event),
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Errors: make(chan error),
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done: make(chan struct{}),
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doneResp: make(chan struct{}),
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}
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w.cv = sync.NewCond(&w.mu)
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go w.readEvents()
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return w, nil
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}
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func (w *Watcher) isClosed() bool {
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select {
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case <-w.done:
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return true
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default:
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return false
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}
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}
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// Close removes all watches and closes the events channel.
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func (w *Watcher) Close() error {
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if w.isClosed() {
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return nil
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}
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// Send 'close' signal to goroutine, and set the Watcher to closed.
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close(w.done)
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// Wake up goroutine
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w.poller.wake()
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// Wait for goroutine to close
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<-w.doneResp
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return nil
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}
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// Add starts watching the named file or directory (non-recursively).
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func (w *Watcher) Add(name string) error {
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name = filepath.Clean(name)
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if w.isClosed() {
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return errors.New("inotify instance already closed")
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}
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const agnosticEvents = unix.IN_MOVED_TO | unix.IN_MOVED_FROM |
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unix.IN_CREATE | unix.IN_ATTRIB | unix.IN_MODIFY |
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unix.IN_MOVE_SELF | unix.IN_DELETE | unix.IN_DELETE_SELF
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var flags uint32 = agnosticEvents
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w.mu.Lock()
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watchEntry, found := w.watches[name]
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w.mu.Unlock()
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if found {
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watchEntry.flags |= flags
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flags |= unix.IN_MASK_ADD
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}
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wd, errno := unix.InotifyAddWatch(w.fd, name, flags)
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if wd == -1 {
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return errno
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}
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w.mu.Lock()
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w.watches[name] = &watch{wd: uint32(wd), flags: flags}
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w.paths[wd] = name
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w.mu.Unlock()
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return nil
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}
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// Remove stops watching the named file or directory (non-recursively).
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func (w *Watcher) Remove(name string) error {
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name = filepath.Clean(name)
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// Fetch the watch.
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w.mu.Lock()
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defer w.mu.Unlock()
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watch, ok := w.watches[name]
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// Remove it from inotify.
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if !ok {
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return fmt.Errorf("can't remove non-existent inotify watch for: %s", name)
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}
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// inotify_rm_watch will return EINVAL if the file has been deleted;
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// the inotify will already have been removed.
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// watches and pathes are deleted in ignoreLinux() implicitly and asynchronously
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// by calling inotify_rm_watch() below. e.g. readEvents() goroutine receives IN_IGNORE
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// so that EINVAL means that the wd is being rm_watch()ed or its file removed
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// by another thread and we have not received IN_IGNORE event.
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success, errno := unix.InotifyRmWatch(w.fd, watch.wd)
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if success == -1 {
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// TODO: Perhaps it's not helpful to return an error here in every case.
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// the only two possible errors are:
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// EBADF, which happens when w.fd is not a valid file descriptor of any kind.
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// EINVAL, which is when fd is not an inotify descriptor or wd is not a valid watch descriptor.
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// Watch descriptors are invalidated when they are removed explicitly or implicitly;
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// explicitly by inotify_rm_watch, implicitly when the file they are watching is deleted.
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return errno
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}
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// wait until ignoreLinux() deleting maps
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exists := true
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for exists {
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w.cv.Wait()
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_, exists = w.watches[name]
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}
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return nil
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}
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type watch struct {
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wd uint32 // Watch descriptor (as returned by the inotify_add_watch() syscall)
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flags uint32 // inotify flags of this watch (see inotify(7) for the list of valid flags)
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}
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// readEvents reads from the inotify file descriptor, converts the
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// received events into Event objects and sends them via the Events channel
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func (w *Watcher) readEvents() {
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var (
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buf [unix.SizeofInotifyEvent * 4096]byte // Buffer for a maximum of 4096 raw events
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n int // Number of bytes read with read()
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errno error // Syscall errno
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ok bool // For poller.wait
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)
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defer close(w.doneResp)
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defer close(w.Errors)
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defer close(w.Events)
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defer unix.Close(w.fd)
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defer w.poller.close()
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for {
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// See if we have been closed.
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if w.isClosed() {
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return
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}
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ok, errno = w.poller.wait()
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if errno != nil {
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select {
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case w.Errors <- errno:
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case <-w.done:
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return
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}
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continue
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}
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if !ok {
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continue
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}
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n, errno = unix.Read(w.fd, buf[:])
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// If a signal interrupted execution, see if we've been asked to close, and try again.
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// http://man7.org/linux/man-pages/man7/signal.7.html :
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// "Before Linux 3.8, reads from an inotify(7) file descriptor were not restartable"
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if errno == unix.EINTR {
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continue
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}
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// unix.Read might have been woken up by Close. If so, we're done.
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if w.isClosed() {
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return
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}
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if n < unix.SizeofInotifyEvent {
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var err error
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if n == 0 {
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// If EOF is received. This should really never happen.
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err = io.EOF
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} else if n < 0 {
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// If an error occurred while reading.
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err = errno
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} else {
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// Read was too short.
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err = errors.New("notify: short read in readEvents()")
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}
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select {
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case w.Errors <- err:
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case <-w.done:
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return
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}
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continue
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}
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var offset uint32
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// We don't know how many events we just read into the buffer
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// While the offset points to at least one whole event...
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for offset <= uint32(n-unix.SizeofInotifyEvent) {
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// Point "raw" to the event in the buffer
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raw := (*unix.InotifyEvent)(unsafe.Pointer(&buf[offset]))
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mask := uint32(raw.Mask)
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nameLen := uint32(raw.Len)
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// If the event happened to the watched directory or the watched file, the kernel
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// doesn't append the filename to the event, but we would like to always fill the
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// the "Name" field with a valid filename. We retrieve the path of the watch from
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// the "paths" map.
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w.mu.Lock()
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name := w.paths[int(raw.Wd)]
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w.mu.Unlock()
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if nameLen > 0 {
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// Point "bytes" at the first byte of the filename
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bytes := (*[unix.PathMax]byte)(unsafe.Pointer(&buf[offset+unix.SizeofInotifyEvent]))
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// The filename is padded with NULL bytes. TrimRight() gets rid of those.
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name += "/" + strings.TrimRight(string(bytes[0:nameLen]), "\000")
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}
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event := newEvent(name, mask)
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// Send the events that are not ignored on the events channel
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if !event.ignoreLinux(w, raw.Wd, mask) {
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select {
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case w.Events <- event:
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case <-w.done:
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return
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}
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}
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// Move to the next event in the buffer
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offset += unix.SizeofInotifyEvent + nameLen
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}
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}
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}
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// Certain types of events can be "ignored" and not sent over the Events
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// channel. Such as events marked ignore by the kernel, or MODIFY events
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// against files that do not exist.
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func (e *Event) ignoreLinux(w *Watcher, wd int32, mask uint32) bool {
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// Ignore anything the inotify API says to ignore
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if mask&unix.IN_IGNORED == unix.IN_IGNORED {
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w.mu.Lock()
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defer w.mu.Unlock()
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name := w.paths[int(wd)]
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delete(w.paths, int(wd))
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delete(w.watches, name)
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w.cv.Broadcast()
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return true
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}
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// If the event is not a DELETE or RENAME, the file must exist.
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// Otherwise the event is ignored.
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// *Note*: this was put in place because it was seen that a MODIFY
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// event was sent after the DELETE. This ignores that MODIFY and
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// assumes a DELETE will come or has come if the file doesn't exist.
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if !(e.Op&Remove == Remove || e.Op&Rename == Rename) {
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_, statErr := os.Lstat(e.Name)
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return os.IsNotExist(statErr)
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}
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return false
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}
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// newEvent returns an platform-independent Event based on an inotify mask.
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func newEvent(name string, mask uint32) Event {
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e := Event{Name: name}
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if mask&unix.IN_CREATE == unix.IN_CREATE || mask&unix.IN_MOVED_TO == unix.IN_MOVED_TO {
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e.Op |= Create
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}
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if mask&unix.IN_DELETE_SELF == unix.IN_DELETE_SELF || mask&unix.IN_DELETE == unix.IN_DELETE {
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e.Op |= Remove
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}
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if mask&unix.IN_MODIFY == unix.IN_MODIFY {
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e.Op |= Write
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}
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if mask&unix.IN_MOVE_SELF == unix.IN_MOVE_SELF || mask&unix.IN_MOVED_FROM == unix.IN_MOVED_FROM {
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e.Op |= Rename
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}
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if mask&unix.IN_ATTRIB == unix.IN_ATTRIB {
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e.Op |= Chmod
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}
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return e
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}
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